Mammalian Herbivores as Drivers of Community Assembly

Despite growing interest in trait-based approaches to community assembly, little attention has been given to mammalian herbivores and their effects on trait distribution patterns. Large herbivores can play a key role in structuring communities, affecting community assembly though their role as consumers, depositors of metabolic wastes and as agents of disturbance. This study analyzes the effect of a native, reintroduced herbivore on taxonomic and functional trait distributions using a 20-year-old exclosure experiment, stratified across a heterogeneous coastal ecosystem. I found that herbivores can alter the taxonomic diversity, functional composition (CWMs) and functional diversity (FDis) of plant communities, and that their influence may be mediated by the local environmental conditions (soil formation). Importantly, we found significant changes in functional diversity due to elk shifting the dominance of plant species across the landscape even though elk had no influence on species richness. Specifically, I found that elk altered the functional diversity of these plant communities by shifting functional strategies from a stress avoidant strategy to a more resource acquisitive strategy and by deterministically changing functional diversity patterns. Assessing the degree to which herbivores drive community assembly and functional traits has important implications: it provides insights into the mechanisms driving changes in plant communities and has the potential to allow perturbations in communities to be detected and mitigated.